Many types of temporary, movable structures are known in the art. One kind of movable structure comprises a plurality of spaced apart frame members, such as arches, and a membrane stretched over the frame members to create an interior space underneath.
Such structures can have many different types of doors to allow access to the interior space. One type of door known in the art is a so-called “clamshell” door, in which a rounded end of the structure is rotated upward, providing access to the interior space of the structure. Clamshell doors can be implemented by providing a frame member that forms a rounded surface at one end (or both ends) of the structure. The frame member is movable between a closed position, in which the rounded surface closes off an opening to the structure, and an open position, in which the frame member is moved upwardly and either collapses into a compressed position adjacent to one of the plurality of arches, or is positioned above the structure. In either case, in the open position the rounded surface created by the frame member does not close off the opening to the structure. To complete the clamshell door, the membrane of the structure is extended over the rounded surface formed by the frame member when the frame member is in the closed position.
One problem with known clamshell doors for movable structures is that the membrane covering the clamshell door is untensioned, and allowed to drape or baffle when the door is opened. Slack in the membrane is a problem because it makes the membrane much more susceptible to damage. This problem is magnified in structures deployed in hot climates, where the clamshell door is often kept in the open position, with a slack membrane, for extended periods of time. Under such conditions, the useful life expectancy of the membrane is greatly reduced, often by as much as 90%. This problem also is prevalent in cold climates, where the slack membrane is susceptible to cold cracking.